* {
margin: 0;
padding: 0;
}

body, html {
font-family: Calibri, "times new roman", sans-serif;
}

#button {
margin: 5% auto;
width: 100px;
text-align: center;
}

#button a {
background-image: linear-gradient(to bottom,#2a95c5,#21759b);
background-image: -o-linear-gradient(to bottom,#2a95c5,#21759b);
background-image: -ms-linear-gradient(to bottom,#2a95c5,#21759b);
background-image: -moz-linear-gradient(to bottom,#2a95c5,#21759b);
background-image: -webkit-linear-gradient(to bottom,#2a95c5,#21759b);
background-color: #2e9fd2;
width: 86px;
height: 30px;
vertical-align: middle;
padding: 10px;
color: #fff;
text-decoration: none;
border: 1px solid transparent;
border-radius: 5px;
}

#popup {
width: 100%;
height: 100%;
position: fixed;
background: rgba(0,0,0,.7);
top: 0;
left: 0;
z-index: 9999;
visibility: hidden;
}

.window {
width: 650px;
height: 240px;
background: #fff;
border-radius: 10px;
position: relative;
padding: 10px;
box-shadow: 0 0 5px rgba(0,0,0,.4);
text-align: center;
margin: 15% auto;
}

.close-button {
width: 20px;
height: 20px;
background: #000;
border-radius: 50%;
border: 3px solid #fff;
display: block;
text-align: center;
color: #fff;
text-decoration: none;
position: absolute;
top: -10px;
right: -10px;
}

#popup:target {
visibility: visible;
}